I am about to lose my mind here. My car overheated the other day so I pulled the water pump and installed a new one. I also replaced the thermostat(made sure it was in the correct way) and put everything back together. Started the car, vented out all the air, and it still OVERHEATS! I am clueless. The water is getting hot cause the expansion tank level is rising and if there was air in the system, that is what the little bypass is for on the thermostat. I am clueless as to what is the problem. Not a blown head gasket, no leaks.... I have no idea. The temp in the motor goes up but the hoses to the radiator never get warm. I checked the supercharger gears- didn't break open the little gearbox, but with the pump off I put a little weight against the gear and bumped the car over and it pushed with plenty of force, more than enough to turn the pump. I know the temp gauge is right too cause i checked it with an OBD scanner too. It is getting hot, but not circulating water to cool down. I even checked the old water pump and I boiled the old thermostat and it oped up just fine. Please help me.....

 

When you changed everything, did you flush the system with a flush kit? It seems highly unlikely, but there might be a blockage in there somewhere.

On a related note, does the radiator fan work?

 

As nabeshin said are your rad fans coming on as the car begins to heat up? What year is your Mini?

 

I would check the fan unit. It has 2 stage operation - low & high. Low Stage can be activated by turning ON the AC or by temperature at 106*C. Stage 2 (high) kicks in at 112*C.

Is the impeller on the waterpump made of plastic? If yes, was it broken with missing parts? If yes, you may have blockage in the system.

 

No broken impeller pieces. Disassembled the old pump and checked that too. Both stages of the fan are working properly. Only one fan. 2005 MCS.

 

OK got it fixed. I know I sound stupid but I guess I did not get all of the air out of the lines. I opened the little vent screw untill nothing but water was coming out and then topped of the reservoir. No more problems. I think it was just a sluggish thermostat....but I changed the pump anyways for piece of mind. I remember now that I filled the coolant with the front on jackstands and even started it, so when I thought it was full, there was still a bubble. Yeah I know dumb.....if anyone has ever changed one of these things....you know it is an easy mistake...by the time you finally get it all back together, you just want to get done. thanks for all the help especially k-huevo.

 

I never noticed on the MINI, but a lot of todays cars have a vent that must be opened to completely fill the cooling system after it's been drained. If this isn't done the car will overheat.

If this doesn't apply to the MINI remember, I was just trying to help.

 

THIS DEFINITELY APPLIES!!!

 

Remember on a MCS, there are 2 bleed screws. One is easily accessible on the upper radiator hose. The other is down a ways under the right side of the plastic intercooler cover. If you bleed the first one, you will still over heat since the other is still air locked. Trust me, I know.

 

This also applies to the second generation MINI's the only difference is ONE bleed screw that's easily accessible.